Stop updating FileSelection when not changed.

ui/file_manager/file_manager/foreground/js/file_selection.js

Index: ui/file_manager/file_manager/foreground/js/file_selection.js
diff --git a/ui/file_manager/file_manager/foreground/js/file_selection.js b/ui/file_manager/file_manager/foreground/js/file_selection.js
index fa7a0529a9dbbf88c8f845c1d62835e6a748c450..df2bc0726fe4ddde1f4ad2a498077bf975e62bf2 100644
--- a/ui/file_manager/file_manager/foreground/js/file_selection.js
+++ b/ui/file_manager/file_manager/foreground/js/file_selection.js
@@ -180,6 +180,16 @@ FileSelectionHandler.prototype.onFileSelectionChanged = function() {
     return /** @type {!Entry} */ (
         this.fileManager_.getFileList().item(index));
   }.bind(this));
+
+  var isSelectionChanged = (indexes.length !== this.selection.indexes.length);
+  for (var i = 0; i < indexes.length && !isSelectionChanged; i++) {

[hirono, 2017/04/21 04:55:03]

Sorry one more thing. The selection change like [0, 1] -> [1, 0] can happen? If
so, can we skip dispatching events for this case as well?

[tetsui2, 2017/04/21 05:15:35]

It's okay to overlook some non-changes unless it's fired repeatedly.
I don't think it would happen. I also tried to select files and then change the
ordering but the event didn't fire.

+    if (entries[i].toURL() !== this.selection.entries[i].toURL()) {

[fukino, 2017/04/21 05:44:31]

nit: Let's extract a utility function to compare two entry arrays (like
util.isSameEntries) in ui/file_manager/common/js/util.js, and use
util.isSameEntry inside it.

+      isSelectionChanged = true;
+    }
+  }
+  if (!isSelectionChanged) {
+    return;
+  }
   this.selection = new FileSelection(indexes, entries);
 
   if (this.selectionUpdateTimer_) {